1. Field of the Invention
The present invention relates to a sheet conveying device for conveying sheets in a vertical direction (gravitational direction) and to an image forming apparatus equipped with this sheet conveying device.
2. Description of the Related Art
As shown in FIG. 22, in a conventional sheet conveying device, there are arranged two pairs of rollers: a lower pair of rollers 1, 2 and an upper pair of rollers 3, 4, and a sheet is conveyed from the lower roller pair 1, 2 to the upper roller pair 3, 4. Between the lower roller pair 1, 2 and the upper roller pair 3, 4, there is provided a conveyance guide 54 for guiding the sheet.
In a conventional construction, this conveyance guide 54 is formed such that the bending point (the drawing shows an end of the bending line) X between the n-th surface immediately before the upper roller pair 3, 4 and the (nxe2x88x921)th surface therebelow is above the intersection Y of the nip plane 110 of the lower roller pair 1, 2 (the tangent plane at the nip portion of the lower roller pair 1, 2) and the nip plane 120 the upper roller pair 3, 4 (the tangent plane at the nip portion of the upper roller pair 3, 4) (the drawing shows an end of the intersection line of the nip planes 110 and 120). In this construction, the n-th surface of the conveyance guide 54 causes the leading end of the sheet to positively abut the outer periphery of the roller 4, whereby conveyance is effected with the leading end of the sheet being directed in a stable manner.
The above-described prior-art technique, however, has the following problems.
When a sheet 70 is guided by the conventional conveyance guide 54, the sheet 70 is allowed, for example, to be raised from the conveyance guide 54, resulting in a rather unstable conveyance. Thus, the sheet 70 does not smoothly enter the nip portion of the upper roller pair 3, 4, causing jamming or the like.
Further, when this conveyance guide 54 is provided on the downstream side of a fixing roller pair of an image forming apparatus, the raised sheet abuts the fixing roller, and an unfixed toner image on the sheet is scattered by a shock of collision, resulting in a transfer deviation (hereinafter referred to as image shock).
The present invention has been made with a view toward solving the above problems in the prior art. It is an object of the present invention to provide a sheet conveying device and an image forming apparatus capable of vertically conveying sheets in a stable manner.
In accordance with the present invention, there is provided a sheet conveying device, including: upper and lower roller pairs; and a conveyance guide provided between the roller pairs and adapted to guide a sheet conveyed from the lower roller pair toward the upper roller pair, wherein the conveyance guide has first and second guide surfaces for guiding the sheet which consist of two surfaces arranged vertically so as to intersect each other, wherein the intersection of the first and second guide surfaces is situated above the intersection of the nip plane of the lower roller pair and the nip plane of the upper roller pair, and wherein the intersection of the first and second guide surfaces is situated in a region on the side opposite to the direction in which the guided sheet is separated from the conveyance guide with respect to the nip plane of the lower roller pair and the nip plane of the upper roller pair.